1. Field of the Invention
The present invention pertains to intraocular lenses within the posterior chamber, and more particularly, to aspheric, conic, or prolate intraocular lenses within the posterior chamber.
2. Description of Related Art
It is often the case that an elderly patient will develop a condition called a cataract in the eye's crystalline lens. The cataract can develop to such a state that vision quality is significantly diminished to the point where surgical intervention is required to restore clear vision. In this surgical intervention, the crystalline lens containing the cataract is removed and an artificial lens is implanted. This artificial lens is called an intraocular lens (IOL). The IOL can be made of various materials, and its optical surfaces can be very simple such as planes, spheres, or torics, or the surfaces can be quite complex and even designed for a specific eye. The goal of the IOL design is, of course, to provide the patient with good vision quality. This means that the optical aberrations (deviation from a perfect focus) should be small. Over the last few decades the goal has been to provide the patient with a lens that significantly removes defocus and astigmatism. More recently, there has been an effort to remove other (higher-order) aberrations, such as spherical aberrations, through the IOL design.
The eye can be considered as an optical system with its specific set of ocular aberrations. Since the normal cornea adds positive spherical aberration, it is possible to design an IOL with negative spherical aberration to reduce the normal eye's total spherical aberrations. If the lens is placed in the correct position and orientation in a normal eye, the spherical aberrations will be reduced as desired. This is the ideal situation. However, it is often the case that a patient's eye will have a cornea that has had refractive surgery such as LASIK, PRK, or RK. In addition, the lens may be decentered or tilted within the eye. In these non-ideal situations, the patient's vision will no longer have the desired improvement over the traditional spherical lenses. If the situation is far enough from the ideal, the patient's vision would have been better with a traditional spherical IOL rather than the “improved” IOL designed for reduction of spherical aberration.
It is possible to consider a reasonable amount of IOL decentration and tilts during the design process and so develop an IOL that is more tolerant to these types of situations. Such considerations can lead to an IOL design where very little positive spherical aberrations are added to the positive spherical aberrations generated by the typical cornea. However, the IOL would not necessarily have the benefit of being an equal surface (both surfaces are the same) optic. Also, the amount of spherical aberration for the IOL should be the same for each lens power provided so that postoperative results are more predictable. This can be measured using the longitudinal ray aberrations for the IOL. It is the objective of the present invention to provide a foldable IOL design that retains the benefits of an aspheric IOL that reduces spherical aberrations and additionally, is an equal surface design and has the same longitudinal ray aberrations characteristic for each IOL power.